Japanese Utility Model Application Public Disclosure (Kohkai publication) No. 59-190648 discloses a typical retractable wiper apparatus of the type described, as shown in FIGS. 19 to 21 attached to the present application.
More specifically, the prior art wiper apparatus illustrated therein comprises a first crank 2 connected to and locked by a nut 4 to an output shaft 1 of a reducer which is in turn connected to a wiper motor (not shown), and a second crank 3 which is secured to the first crank by means of a first threaded pivot shaft 5 projecting from the second crank and a nut 6. The first crank 2 is formed with stop shoulders 7 and 8 having locking recesses 7a and 8a, respectively. Secured to the second crank 3 is a second pivot shaft 9 over which a cam 10 is fitted. A bearing 11 is also fitted over the pivot shaft 9 and secured integrally to the cam 10. A first link 12 is secured to the bearing 11 by means of a socket 13 which is connected to the link 12 and adapted to receive the bearing 11.
A wiper blade 14 is supported by a wiper arm 15 which is secured at a pivot 16 to a second link 17 which is in turn connected to the first link 12. A detent 18 engageable with locking recesses 7a, 8a is slidably mounted in a guide frame 20 and is biased outwardly by a spring 19. The frame 20 is fastened to the second crank 3 by screws 21.
During the normal wiping operation the motor output shaft 1 is rotated in the forward direction of rotation as indicated by the arrow P in FIG. 21. The rotation of the first crank 2 in this direction initially causes the second crank 3 connected by links 12 and 17 to the wiper arm 15 to be relatively rotated about the pivot shaft 5 due to the rotational resistance of the second crank 3 until the second crank is bent relative to the first crank and comes into abutment with the stop shoulder 8 of the first crank 2, whereupon the detent 18 is urged into the recess 7a to lock the second crank to the first crank at said bent angle. While angled relative to the first crank 2 as shown in FIG. 21, the second crank 3 is thus rotated about the output shaft 1 in the direction P, whereby the pivot pin 16 is moved in its reciprocal rotating motion by means of the links 12, 17 to operate the wiper blade 14 for wiping action.
The range in which the wiper blade 14 is reciprocally moved with the second crank 3 angled relative to the first crank 2 is a normal range of operation. Upon the wiper motor being deenergized, the wiper blade is stopped at the extreme end A of the normal range of operation by a conventional automatic stopping-at-fixed position mechanism (not shown).
When it is desired to stow away or retract the wiper arm 15 from its normal stop position A, the wiper motor is driven in the reverse direction, so that the first crank 2 is rotated in a direction opposite from that indicated by the arrow P. The second crank 3 which is connected to the wiper blade 14 by means of the links 12, 17 is caused to relatively rotate about the pivot shaft 5 due to the rotational resistance until the crank 3 comes into abutment with the stop shoulder 7 of the first crank 2 to assume the straight extended position whereupon the detent 18 is urged into the recess 8a to lock the second crank at its extended position.
The effective length of the cranks when the second crank 3 is extended straight relative to the first crank 2, that is, the distance between the two shafts 1 and 9 is longer than the distance between the two shafts 1 and 9 when the second crank is at its angled position, so that the wiper blade 14 at its normal stop position A in FIG. 21 is retracted beyond its normal range of operation into the retracted or concealed position B.
During the wiping and blade retracting operations the cam 10 fitted over the pivot shaft 9 of the second crank 3 is rotated in unison with the link 12. The cam 10 is adapted to press and lock the detent 18 which is in engagement with the recess 7a during the forward rotation for the wiping operation and to disengage from the detent upon reverse rotation through some degrees of angle (about 35.degree.) of the cam 10 after the normal rotation (180.degree.), and then to press and lock the detent 18 as it is engaged with the recess 8a when the second crank 3 is completely extended relative to the first crank.
While the prior art retractable wiper apparatus described above is capable of retracting the wiper blade from the normal stop position A into the retracted position B by means of the relatively simple mechanism, during the normal continuous driving of the motor (wiper operation) with the second crank 3 bent at the predetermined angle relative to the first crank 2 such condition occurs once per rotation of the cam that the cam 10 is disengaged from pressing contact with the detent 18. In such condition there is instability in operation in that the biasing force of the spring 19 alone is relied on for urging the detent 18 into the recess 7a of the stop shoulder 7. As a result, play or creaking tends to occur, causing clattering at the tip of the wiper blade and making the automobile driver feel uneasy.